A business of an enterprise has been rapidly expanded due to an explosive increase of data and the appearance of various environments and platforms. With the advent of a new business environment, more efficient and flexible processing of a data service and information and data management function are required. According to such a change, a research into a database for solving problems in high performance, high availability and extensibility which are a basis of enterprise business implementationhas continued.
In the database management system (DBMS), data can be stored in a data storage. In a relational database management system (RDBMS), the data storage may be designated as a table. The table can include one or more rows and each of one or more rows can include one or more columns.
A query language for a database as a structured query language (SQL) can be used to construct and utilize the database. The SQL can include a data definition language (DDL) and a data manipulation language (DML).
In a conventional SQL grammar, in order to verify a result for a subquery, the result cannot but be separately verified by separately performing the corresponding subquery apart from a main query. For example, a result of a specific query for the database may be abruptly abnormal. In this case, inspecting multiple tables included in the specific query is required to verify a cause of the abnormal result. The inspection can generally be performed by a scheme that inspects a table(s) associated with respective sub queries while individually performing only a subquery for a complicated query. However, such a scheme may not be appropriate under environments described below.
A first environment is a case in which the query is performed in an application. In this case, it may not be easy to configure an environment which is the same as an environment in which the query result is abnormal.
A second environment is a case in which the query is very complicated. A situation in which it is difficult to independently separate the query like a correlated subquery, or the like according to a type of query may occur. In this case, since the query is not a simple subquery type, it is not easy to verify contents.
A third environment is a case in which a lot of time is required for processing the query. In the case of a complicated query which accesses the multiple tables, even though the main query is divided into the sub queries to be respectively performed, a time which is approximately several times longer than a total execution time is required.